This proposal is for renewal of a current research grant which is concerned with several aspects of the natural polyglutamate forms of folic acid in tissues and the proteins which bind them in vivo. We propose to carry out the following studies. (1) During the current grant period we have identified the mitochondrial folate binding protein of rat liver to be two separate enzymes: dimethylglycine dehydrogenase and sarcosine dehydrogenase. We shall characterize the reactions catalyzed by these two enzymes and elucidate the role of folate in the metabolism of the one-carbon units produced. (2) During the current grant period we have purified and partially characterized a folate binding protein from rat liver cytosol which has a molecular weight of about 150,000. This protein has no demonstrable enzyme activity. We will evaluate the possibility that this protein is involved with folate storage by measuring the relative rates of ligand depletion during folate deficiency and repletion during folate refeeding. We will also measure the maximum binding capacity of this protein. (c) We shall characterize the high molecular weight (approximately 300,000 dalton) species in rat liver cytosol which has folate binding activity. This protein rapidly binds folate following injection of tritiated folic acid. We shall use the techniques of protein purification and ligand identification which have been successful in our current work.